A battery separator is a membrane between a positive electrode and a negative electrode of a battery and is a critical component in a battery. The main functions are to separate a positive electrode and a negative electrode of the battery from each other to disable free electronic transport within the battery, but to enable free ionic transport of electrolyte between the electrodes. Performance of a battery separator determines the battery interface structure and the battery internal resistance, and further affects the battery performance, such as capacity, cycle performance, and current density during charging and discharging.
A battery separator is usually made from polypropylene and polyethylene. However, the battery separator made from polypropylene and polyethylene has a drawback in affinity for electrolyte, such as low electrolyte absorption, low surface energy and high heat shrinkage rate. The battery separator shrinks greatly when heated over 100° C. which results in a short circuit between the battery electrodes.
In the prior art, a separator substrate made from polypropylene and polyethylene may be coated on the surface with inorganic particles, such as silica and calcium carbonate, thereby lessening heat shrinkage of the battery separator to a certain degree. However, improvement on the battery performance after adopting this method is limited, moreover, the battery cycle and security performance are difficult to be improved.